// Undefined variable let a; if (a == null) { console.log('Null or undefined value!'); } else { console.log(a); } This would check whether a is either null or undefined. Since a is undefined, this results in: Null or undefined value! ADVERTISEMENT Though, we don't really kn...
In the above example, we have used the first if statement to check if the "a" variable is either undefined or null. If it satisfies either of the conditions, then the if block will execute; otherwise, the else block will execute. In the second statement, we have used the if statement ...
if(typeof(sTip)!="undefined"&&sTip!=null){ return sTip; } else { return ""; } } /* * 显示错误 */ function showMessage(){ //外接显示错误函数 if(typeof(me.showMessageEx)=="function"){ return me.showMessageEx(me.message); } if(me.alert==true){ alert(me.message); } else { v...
The falsy values in JavaScript are: null, undefined, false, 0, NaN (not a number), "" (empty string). If you have to do this often, define a reusable function. index.js function isTruthyOrZero(value) { return Boolean(value || value === 0); } console.log(isTruthyOrZero(0)); ...
undefined . The value null is falsy, but empty objects are truthy, so typeof maybeNull === "object" && !maybeNull is an easy way to check to see that a value is not null . Finally, to check if a value has been declared and assigned a value that is neither ...
isNonEmpty:function(value, errorMsg) {//不能为空errorMsg = errorMsg||" ";if(!value.length)returnerrorMsg; }, minLength:function(value, length, errorMsg) {//大于errorMsg=errorMsg||" ";if(value.length < length)returnerrorMsg; }, ...
Just as with keys - if an object has novaluesassociated (not even anundefined/null) - it's empty: constisEmptyObject =(obj) =>{returnObject.values(obj).length ===0&& obj.constructor ===Object; }console.log(isEmptyObject(emptyObject));// true ...
TheObject.fromEntries()transforms a list of key-value pairs into an object. I wrotea bookin which I share everything I know about how to become a better, more efficient programmer. You can use the search field on myHome Pageto filter through all of my articles. ...
getMessage(err)- Retrieves the message of an error orerritself if it's a String. Iferrorerr.messageis undefined we return an empty String. varcheckError=require('check-error'); .compatibleInstance(err, errorLike) varcheckError=require('check-error');varfuncThatThrows=function(){thrownewType...
Undefined NaN Now, look at the discussed approaches! Approach 1: Check if a Value is Falsy in JavaScript Using if/else Condition “Logical” operators are used to analyze the logic between values. More specifically, the logical “not(!)” operator gives the value “true” if a falsy value...